GNSS
How it works
Each satellite broadcasts a precisely time-stamped ranging signal and a navigation message describing its own orbit and clock. The receiver measures signal travel time (pseudoranges) to the visible satellites; at least four satellites are required to solve the 3D position plus the receiver clock bias. Differential corrections (DGNSS) and carrier-phase measurements cancel common errors; RTK resolves the carrier-phase integer ambiguity using corrections from a base station or an NTRIP network, achieving centimeter accuracy. Multi-frequency (L1/L2/L5) and multi-constellation operation improve availability and accuracy, and a dual-antenna configuration lets the system derive vehicle heading/orientation.
Problem solved
Before GNSS, obtaining absolute global position required ground-based radio beacons with limited range or dead reckoning, whose error grows over time. GNSS delivers continuous, global, all-weather position, velocity and precise time anywhere with a clear sky view.
Components
Constellation of medium-Earth-orbit satellites broadcasting ranging signals and navigation messages.
Ground monitoring stations and a master control station that track satellites, compute their orbits and clocks, and upload corrections.
GNSS receivers that capture signals from multiple satellites and compute position, velocity and time.
Official
Implementation
Signals reflected off buildings and surfaces introduce position errors.
Tall buildings and terrain block or attenuate satellite signals, degrading solution geometry.
Ionospheric and tropospheric refraction delay signals; mitigated by multi-frequency reception or corrections.
Weak GNSS signals are vulnerable to jamming and falsification, threatening autonomous systems.
RTK requires corrections from a nearby base station or NTRIP network; accuracy degrades with distance and needs re-fixing of phase ambiguities.
Evolution
Beginning of practical satellite navigation.
Hyperparameters (configurable axes)
Positioning method that determines accuracy — from standalone to differential and carrier-phase.
Number of bands used; multi-frequency operation reduces ionospheric error.
Number of constellations used; multi-constellation operation improves availability and accuracy.